According to the Standard GB3836.1-2010 for the Interlocking Device, it requires that the structure of an interlocking device should guaranty that its functions cannot be removed easily by non-dedicated tools, to maintain the interlocking device specially for explosion protection. According to the Requirement of the Rule 445 in Safety Regulations in Coal Mine, lock devices of all switches must reliably prevent power from being transmitted unauthorized and prevent open operation from being performed unauthorized. Currently, in various explosive hazardous areas, especially in electric apparatuses used for underground coal mine, a dual-prevention lock is mounted on the locking device of the electric apparatuses for preventing open operation from being performed unauthorized by unprofessional person and for preventing power from being transmitted unauthorized (referred to as “dual-prevention”), thereby ensuring the safe usage of the electric apparatuses.
A Chinese patent ZL 200620024380.3 discloses a safety lock which requires that a locking opening must be machined in a locked screw of an explosion-proof electric equipment. However, there will be a situation occurring that the locking opening is not machined by workers as required in practical installation process, resulting in that the safety lock fails, without preventing power from being transmitted unauthorized and preventing open operation from being performed unauthorized. Thereby there is potential safety hazard.